Identification of semiochemicals for detection and monitoring of the walnut twig beetle, Pityophthorus juglandis (Coleoptera: Scolytidae)

The walnut twig beetle (WTB), Pityophthorus juglandis, is associated with thousand cankers disease of walnut (Juglans sp.). Spores of the pathogenic fungus, Geosmithia morbida, are introduced into the phloem when the beetles bore through the bark. The infection results in numerous cankers that eventually kill the tree. The WTB is expanding its range and causing increased tree mortality in the western U.S. Little is known about the semiochemicals that mediate the colonization of host trees by WTB. Trees are initially colonized by male WTB, which then release pheromones attractive to both sexes. Arriving females also contribute to the aggregation pheromone. We collected volatiles on Porapak Q from male or female WTB feeding on J. hindsii branches, and from the branches alone. Pentane extracts of the Porapak were analyzed by GC-MS. Four compounds identified in the extracts from males feeding on J. hindsii were not present in extracts from females. Two other compounds of interest were found in extracts from both males and females, and small amounts of one were detected in the walnut alone. One male-produced compound and one compound associated with the males, females, and the branches were shown to be antennally active by GC-EAD. Using yellow sticky card traps and funnel traps, we evaluated these compounds in the field, alone and in combination, as flight attractants for the WTB. Preliminary results indicate that one of the four male-produced compounds is attractive to males and females, and the antennally active compound produced by both sexes is interruptive.